The central objective of the proposed study is to identify and characterize the reaction products of the polycyclic aromatic carcinogens with DNA, both in vivo and in vitro. During the project period it is proposed to use sensitive spectroscopic and chromatographic techniques to characterize the DNA-carcinogen adducts produced in vivo in tissue cultures and in mouse skin. The in vivo reactions are thought to proceed by way of reactive metabolic intermediates of the carcinogens, but very little is known in detail about the structure of these intermediates. It is proposed to identify the major intermediates by comparison of the products of in vivo reactions with the in vitro reaction products of DNA with suspected likely intermediates, synthesized separately. It will then be possible to synthesize, in vitro, large quantitites of DNA adducts which are similar to the adducts produced in vivo. The in vitro reactions and their products will be subjected to detailed kinetic studies and physicochemical analyses. A variety of spectroscopic techniques will utilize the excited singlet and triplet states of the polycyclic aromatic moeities in the DNA-carcinogen adducts as probes of the structure of these complexes. These techniques will include fluorescence and triplet-triplet absorption spectroscopy, optically detected magnetic resonance, and electric-field-induced linear dichroism measurements. To obtain guidelines for the application of these techniques to the covalent adducts, analogous experiments will also be performed with physical intercalation-type complexes of DNA with polycyclic carcinogens and with acridine-type dyes, the structures of which are comparatively better understood.